With a recent tendency to design various electric equipment into micro-electronic forms, demand for a battery, which is small in size, light in weight and thin, and provided with a high energy density. In the field of primary batteries, a small-sized and light-weight battery such as a lithium battery has already been put to practical use. However, its application field has been limited to a small area. In the field of secondary batteries, a battery utilizing a non-aqueous electrolyte, which can be made smaller in size and weight, attracts public attention at present as an alternate battery in place of the conventional lead-battery and a nickel-cadmium battery.
In order to obtain a small-sized and light-weight battery having a high energy density and a high reliability, it is necessary to examine the following problems (1) and (2).
(1) Problem of electrode active material and electrode PA1 (2) Problem of electrolyte PA1 (1) It is hard to increase manufacturing speed because the heating and polymerizing time becomes very long. PA1 (2) It is hard to carry out uniform polymerization because a temperature gradient is apt to be produced in a heating furnace. PA1 (3) The heating furnace and its auxiliary facility become large because the heating must be done in an inert atmosphere. PA1 (4) A cross-linked network structure becomes more irregular because displacement of the polymerization initiator occurs in a liquid composition of the ion-conductive high-molecular compound.
Electrode active materials utilizing intercalation and doping phenomena of the layer compound are especially studied now in many research organizations. These materials are expected to have extremely excellent charge/discharge cycle characteristics, because a theoretically complicated chemical reaction does not take place at the time of the electrochemical reaction in charging and discharging. However, in such electrode active materials, expansion and contraction of the electrode active material occurs when charging and discharging. To cope with this problem, it is required to improve the mechanical strength of the electrode and electrolyte.
A liquid electrolyte, especially prepared by dissolving an ionic compound in an organic electrolyte, has so far been generally used for the electrolyte. However, since there have been problems such as leakage of the electrolyte to the outside of the battery and elusion and evaporation of the electrode material etc. when a liquid electrolyte has been used, problems of inferior long-term reliability and spattering of the electrolyte in the sealing process have remained unsolved. As a means to solve these problems, that is, a means to improve solution-leakage resistance and long-term reliability, an ion-conductive high-molecular compound having a high ionic conductivity has been reported and further studied.
When the ion-conductive high-molecular compound is used as an electrolyte for an electrochemical device, it becomes necessary to make the electrolyte into a film shape in order to reduce internal resistance. This is especially important for a film type battery. In the case of the ion-conductive high-molecular compound, it is possible to work its uniform film easily into a desired shape, and various methods for this purpose are known. Heating and polymerizing has so far been used frequently because of its convenience. However, the heating and polymerizing method has included the following problems.
Incidentally, serious problems were brought about when using the ion-conductive high-molecular compound for the battery. As the charge/discharge cycles were repeated; water was extracted from the cathode composite, this water reached the anode through the electrolyte layer comprising the ion-conductive high-molecular compound, the water reacted with the lithium metal of the anode to produce hydrogen gas, and the pressure inside the battery was increased by this hydrogen gas. As a result, expansion and bursting of the battery took place to impair a long-term reliability and safety.
This invention is made in consideration of the above present circumstances, and an object of it is to provide a battery which does not have the problem of expansion and bursting, thereby improving the long-term reliability and safety, has improved charge/discharge cycle characteristics, and further can make workability better.